Inspections of some of these planted areas after a lapse of from 10 to 15 years indicated that the sites still support only a scant herbaceous cover, with broomsedge and povertygrass predominating, and with no evidence of native woody species encroaching on the areas. The few surviving Asiatic chestnut seedlings were sickly looking, multi-stemmed, misshapen trees, heavily infected with twig blight and chestnut blight, and severely damaged by winter injury. But despite these heavy losses, a few plantations succeeded at least in part, and from these limited areas, together with an appraisal of the situations where some of the earlier planted chestnuts grew well, valuable information as to the site requirements of the Asiatic chestnut species was obtained.
Site Requirements
These field studies clearly showed that the site requirements of the Asiatic chestnuts, particularly with reference to soil moisture, are more nearly like these of yellow poplar, northern red oak, and white ash, than like the American chestnut or the native chinkapin species. On fertile, fresh soils that support the more mesophytic native species, Asiatic chestnuts remained relatively disease-free, developed straight boles, made satisfactory growth, and were able to maintain themselves in the stands in competition with the other rapid-growing associated hardwood species.
The indicator plants that suggest good sites for Asiatic chestnuts are: (a) Tree species—yellowpoplar, northern red oak, white ash, sugar maple, and yellow birch; (b) shrub species—spicebush; (c) herbaceous species—maiden hair fern, bloodroot, jack-in-the-pulpit, squirrelcorn and/or Dutchman's breeches. Plants that indicate sites too dry for forest-tree growth of Asiatic chestnuts are: (a) Tree species—the "hard" pines, black oak and scrub oak; (b) shrub species—dwarf sumac, and low blueberry; and (c) herbaceous species—broomsedge, wild strawberry, and povertygrass. Plants that indicate sites too wet are: (a) Tree species—black ash, red maple, and willows; (b) shrub species—alder; (c) herbaceous species—sedges and skunkcabbage.
Climatic Test Plots
On the basis of the experience gained from the earlier, extensive distribution of Asiatic chestnut planting stock, the Division of Forest Pathology, during the years of 1936, 1938, and 1939, established 21 Asiatic chestnut climatic test plots on cleared forest lands in eight eastern States on the most favorable sites obtainable. These plots, with their isolation borders, aggregating slightly less than 32 acres, and accommodating nearly 22,000 trees spaced 8 by 8 feet, occur from northern Massachusetts, along the Alleghenies southward to the southern Appalachians in southwestern North Carolina, and from the Atlantic seaboard, in southeastern South Carolina through the Middle West to southeastern Iowa. More than 20 strains are being tested at each place, including Chinese, Japanese, Seguin, and Henry species, as well as hybrids, and progeny of some of the oldest introduced chestnuts. Most of the plots are fenced against livestock and deer.
Although the results from these plots are as yet entirely preliminary, during the 8- to 11-year period of testing, valuable information has already been obtained: (1) The range of the Asiatic chestnuts tested does not coincide entirely with the range of the American chestnut or the native chinkapins. All Asiatic chestnut species that have been tested have failed at Orange, Massachusetts, where the American chestnut grew in abundance. In southeastern South Carolina, where the several species of native chinkapin thrive, some of them attaining a height of 20 feet, the Asiatic species have largely failed. On the other hand in northern Indiana and southeastern Iowa, entirely outside the botanical range of the American chestnut, a few Chinese strains have done remarkably well. (2) The Chinese chestnuts have a much wider range adaptability to site than the Japanese chestnuts; the latter are more restricted to mild climate and appear to require somewhat better site conditions. Of ten Chinese strains tested, only four can thus far be recommended for future planting in the Middle West. One Chinese strain that has thus far proven far superior to the others, in all the climatic plots, was introduced by the Department of Agriculture as seed from Nanking, China in 1924. (3) Poorly aerated soil is an important limiting factor in all regions where the chestnuts were tested.
Establishment by Underplanting and Girdling
On the basis of the field experience gained from the wide distribution of Asiatic chestnut planting stock and the information thus far obtained from the climatic test plots, a new method of establishing Asiatic chestnut under forest conditions was initiated in the spring of 1946, and is now being tried on a limited scale. It consists of underplanting, with chestnut seedlings, a fully stocked stand of hardwoods ranging from 4 to 8 inches in diameter breast height in which the predominant species are yellow poplar, northern red oak, white ash, and sugar maples. All overstory growth 5 feet and over in height is then girdled. As the girdled overstory trees die, they gradually yield the site to the planted chestnuts in transition that does not greatly disturb the ecological conditions, particularly of the forest floor. Rapid disintegration of the mantle of leafmold is prevented by the partial shading, which the dead or dying overstory, girdled trees cast. At the same time, the partial shading hinders the encroachment of the sprout hardwoods and the other plant invaders (which would normally become established if the planted area had been clear cut) until the chestnuts have become fully established. Not only does this system provide the best site conditions conducive to the development of forest-tree form in the Asiatic chestnuts, in limited areas, but also under establishment conditions that require a minimum amount of maintenance.
Summary